This invention generally relates to slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which perishable material, such as foodstuff, may be stored.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable fastener elements, or profiles, that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc.
Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 5,809,621 discloses a slider-operated zipper assembly wherein one zipper profile has a pair of handles that cooperate with the slider. As the slider is moved in an opening direction, the handles are squeezed together to disengage the profiles. In U.S. Pat. No. 5,442,838, a slider-operated zipper assembly is disclosed wherein the zipper profiles are engaged and disengaged in the course of a so-called xe2x80x9crolling actionxe2x80x9d. This xe2x80x9crolling actionxe2x80x9d is described as being achieved through cooperation between flanges on the profiles and shoulders that project inwardly from the arms of the slider. U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures. The first profiled structure comprises an interlocking element on a surface directed toward the second profiled structure and an integral base directed away from the second profiled structure. Likewise, the second profiled structure comprises an interlocking element on a surface directed toward the first profiled structure and an integral base directed away from the first profiled structure. Additionally, portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of such reclosable fastener assemblies are the end stops, which prevent the slider from falling off the end of the fastener when the slider reaches the end of the fastener. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; reciprocating anvils, as described in U.S. Pat. No. 5,131,121; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; or plastic end clips fused to the zipper as described in U.S. Pat. No. 5,448,807.
U.S. Pat. No. 5,950,285 discloses a reclosable bag having end stops that prevent a slider from moving beyond the end of the zipper when the slider reaches either the closed or fully open position. The end stops are formed from the material of the zipper profiles and xe2x80x9crise verticallyxe2x80x9d from the zipper to block and prevent further movement of the slider. The end stops are formed by first aligning together the opposing profiles at an end stop area proximate to an end of the bag, and then fusing the zipper profiles at the end stop area to provide a vertical structure for preventing movement of the slider past the ends of the zipper, while at the same time keeping the rails intact. Preferably, the profiles are fused by directing ultrasonic energy to the end stop area. Optionally, the end stops have ridges disposed along their surfaces.
In addition, U.S. Pat. No. 6,357,914 discloses a slider-operated zipper in which the ends of the zipper profiles are deformed or xe2x80x9ccrushedxe2x80x9d to form slider end stops. Preferably, the slider end stops are formed by the application of ultrasonically generated heat and pressure to the ends of the zipper profiles. The sides of the zipper profiles are softened and compressed at end stop areas so as to impart a pre-selected width and an upwelling displacement above the uppermost surfaces of the zipper profiles. The material displaced above the upper surface of the zipper profiles interferes with the top wall and ends of the slider to limit its sideways travel along the zipper. The slider end stops (that is, the deformed portions of the zipper profiles) are configured to avoid deformation of the bottom surfaces of the zipper profiles. The lower ends of the zipper profiles extend undeformed substantially to the side edges of the package. The end stops and the undeformed bottom surfaces of the zipper profiles in the area of end stops cooperate to hold the slider, preventing the slider from being unintentionally derailed. The ""914 patent asserts that separation of the xe2x80x9ccrushingxe2x80x9d operation performed on the zipper profiles to form the slider end stops from the conduction heat sealing operation to form the side seals allows the end stops to be reduced in size, effectively extending the size of the package opening without sacrificing the ability of the end stops to effectively retain the slider on the zipper.
There is a need for a method and an apparatus for ultrasonically deforming the ends of a slider-operated zipper to form structures capable of stopping a slider from sliding off an end of the zipper when incorporated in reclosable packaging.
The invention is directed to a method and an apparatus for ultrasonically stomping the ends of a flexible zipper for forming slider end stops in a reclosable package. The invention is further directed to slider-operated zippers having stomped ends of a particular structure and reclosable packages incorporating such zippers.
One aspect of the invention is an ultrasonic welding assembly comprising a horn and an anvil, wherein the horn comprises a generally T-shaped flattening surface.
Another aspect of the invention is an ultrasonic welding assembly comprising a horn and an anvil, wherein the horn comprises a flattening surface and a plurality of projections projecting out of the flattening surface. Each projection comprises first and second surfaces that are neither parallel nor perpendicular to the flattening surface. The first and second surfaces are inclined at different angles.
Yet another aspect of the invention is an ultrasonic welding assembly comprising a horn having a flattening surface of predetermined shape, an anvil and an anvil cover overlying opposing portions of said anvil, wherein the anvil cover comprises a cutout and the flattening surface of the horn fits in the cutout.
A further aspect of the invention is an assembly comprising a flexible zipper and a slider mounted to the zipper, wherein the zipper comprises a first zipper part comprising a first interlockable element and a second zipper part comprising a second interlockable element, the first and second interlockable elements being mutually interlockable, and the zipper further comprising first and second slider end stops located at opposing ends of the zipper parts, wherein each end stop comprises flattened zipper material having a plurality of spaced spot-shaped indentations.
Yet another aspect of the invention is a package comprising a receptacle, a flexible zipper joined to the receptacle and a slider mounted to the zipper, wherein the zipper has the structure described in the preceding paragraph.
Another aspect of the invention is a method for forming a slider end stop on a flexible zipper. The method comprises the following steps: interlocking first and second parts of a zipper; inserting a slider on the interlocked zipper parts; and transmitting sufficient ultrasonic wave energy into a T-shaped area of the interlocked zipper parts to cause the latter to flatten and fuse in the T-shaped area. The rails of the interlocked zipper parts are undeformed on both sides of a stem of the T-shape.
Other aspects of the invention are disclosed and claimed below.